1. Field of the Invention
The present invention relates to an apparatus and a method for fault-tolerant control in a fault-tolerant control system, into which a fully distributed common memory (FUDCOM) method employing a concurrent write method is realized in the manner of duplication, and more particularly, to a fault-tolerant control system which is allowed to operate as an active processor module or a standby processor module by transferring data from one module to another using extension of memory buses.
2. Description of the Related Art
Full electronic switching systems have been required to have a high reliability and a high availability and have provided fault-tolerant functions by constituting important functions in a duplication manner. Since such systems can be maintained and fixed by an operator when they malfunction due to some errors, they do not require as much a considerable amount of hardware redundancy as has been required in medical equipment, flight control systems, satellites, and military equipment. In general, a switching system is comprised of a module for performing system functions and a standby module for backing up the system functions, and this structure is called a duplication manner.
In a control system realized in the duplication manner by adopting a concurrent write method, consistency of data between two processor modules can be maintained using high-speed data transmission channels. If an error is detected in an active processor module currently performing system functions, the system functions are transferred from the active processor module to a standby processor module which is operating as a system redundancy module so that the error can be fixed without causing discontinuity in a real-time service being provided. In conventional techniques regarding high speed data transmission channels, a method of extending a local bus of a CPU or a memory bus between a memory and a memory controller has been adopted.
In a conventional full electronic switching control system adopting a concurrent write method, a duplicated control system realizes the concurrent write method by extending a local bus or by extending a memory bus. In the duplicated control system adopting a method of extending a local bus, high-speed data transmission channels must be provided. In addition, in the process of realizing such data transmission channels, malfunction of the local bus may be caused by mistakes made by the designer or defects in the elements, and this affects the entire operation of a whole processor module so that the processor module may malfunction or stop operating, and thus the reliability of a system may be degraded. On the other hand, in the duplicated control system adopting a method of extending a memory bus, a memory is divided into a region on which concurrent write can be performed and a region on which concurrent write cannot be performed. Thus, malfunction of a memory and an additional switching time may be needed during the process of switching memories.